Field of the Invention
The present invention relates to an image forming apparatus that prints an image.
Description of the Related Art
Conventionally, there has been known an image forming apparatus, such as a multi-function peripheral and a printer, that is capable of freely switching sheet discharge between face-up discharge and face-down discharge when discharging a sheet onto a discharge tray, by providing an inversion path at a location upstream of a discharge outlet. Further, as an image forming apparatus which is compact in size and performs print processing at a slightly low speed, there is proposed one that has achieved size reduction by omitting the inversion path upstream of the discharge outlet so as to reduce the size of the apparatus. In a case where the inversion path is not provided upstream of the discharge outlet, it is impossible to determine an upward-facing side of a discharged sheet, during the conveying of the sheet for discharging the same onto the discharge tray. To cope with this, there is proposed an apparatus that is configured to make use of a mechanism for double-sided printing, to thereby convey a sheet using a double-sided path (double-sided printing conveying path) so as to change the surface of a sheet on which an image is actually printed, whereby the upward-facing side of the discharged sheet is changed.
For example, in a case where an apparatus configured such that when a sheet subjected to single-sided printing is discharged as it is, the sheet is discharged by “face-down discharge” in which a surface of the sheet having an image formed thereon faces downward on the discharge tray, in order to discharge a sheet by “face-up discharge”, an image is printed on a first surface of the sheet, whereafter the sheet is conveyed along the double-sided path and is discharged without performing printing on a second surface of the sheet. On the other hand, by using the same apparatus, in order to discharge a sheet by face-down discharge according to a double-sided printing job, an image for the reverse side is first printed on a first surface of the sheet, and then an image for the front side is printed on a second surface of the sheet, whereby the sheet is discharged by face-down discharge. If a sheet printed according to a single-sided printing job is discharged by face-up discharge, and a sheet printed according to a double-sided printing job is discharged by face-down discharge, the facing direction of the first surface is opposite between the case of single-sided printing and the case of double-sided printing. To cope with this, in a case where a mixed job mixedly including single-sided printing and double-sided printing is executed on sheets having different directional properties between the front side and the reverse side thereof, such as pre-printed sheets on which an image has been printed in advance, each sheet to be printed by single-sided printing is conveyed through the double-sided path to thereafter print an image for the front side thereof on the second surface thereof, whereby the sheet is discharged by face-down discharge. This makes it possible to make a match in the printed surface between the case of double-sided printing and the case of single-sided printing (cause the first surfaces of the respective sheets to face in the same direction).
On the other hand, there has been known an image forming apparatus that is capable of performing printing on a sheet having directional properties with respect to the orientations (facing directions) of the four sides thereof, such as a pre-punched sheet on which punching has been performed in advance. For example, the pre-punched sheet has punched holes formed in the vicinity of one of the four sides, and the directional properties of the sheet are defined depending on the orientation of the side along which the punched holes are formed. For example, in a case where the side along which the punched holes are formed is oriented (faces) in a direction orthogonal to the conveying direction, whether the side along which the punched holes are formed is at a leading end of the sheet or at a trailing end of the same in the conveying direction has an influence on the relationship between the top and bottom of the sheet and the top and bottom of an image formed thereon. As to such sheets having directional properties, the orientation of sheets set in the sheet feeder has to be changed depending on the sheet conveying path of a printer. To cope with this, there has been proposed an image forming apparatus that allows a user to set sheets having directional properties in the sheet feeder without paying attention to the orientation of the sheets set therein (see Japanese Patent Laid-Open Publication No. 2001-326810). However, in this publication, no description has been made as to double-sided printing, and particularly, there is no reference to a problem of making a match between the orientation of a reference side of a sheet along which punched holes are formed and the orientation of an output image on the sheet, in double-sided printing.